The present invention relates to a safety programmable logic controller (PLC) comprising an I/O module to which a safety device such as an emergency stop switch and a light curtain are connected and a CPU module for executing a safety program for controlling each safety device through the I/O module, and more particularly, to automatically creating the safety program.
Recently, a safety function is commonly introduced into a system controller using a programmable logic controller (hereinafter, referred to as a PLC). The safety function includes, for example, a function for duplexing a CPU, an MPU, or various processing units to allow a processing result to be appropriately output, and a function of halting a system operation based on a predetermined fail safe operation when an emergency condition occurs in a system, and the like. For example, the emergency condition may occur when an emergency stop switch is pressed or when a sensor such as a light curtain detects invasion of a person.
A safety PLC for constructing such a system as disclosed in the patent document 1 is well known in the art.
For example, a standard for creating a safety program has been published from an international electrotechnical commission (IEC). In order to producing a safety program which satisfies this standard, a high level of technical knowledge for the safety program is required.
Meanwhile, in order to reduce the problems relating to productivity or development cost for a sequence program of a general PLC, a programming device has been proposed as disclosed in the patent document 2.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-358106
Patent Document 2: Japanese Unexamined Patent Application Publication H11-3105
However, the related programming device disclosed in the patent document 2 processes a user program (e.g., a sequence program) described by using advanced programming languages such as a C or a ladder. Therefore, users should prepare a user's program by using such a program language.
Additionally, in order to produce a user's program (i.e., the safety program), a user should have a high level of knowledge for a predetermined safety standard, ripe experience for production of the safety program, and the like. Therefore, it requires a long time and a high manufacturing cost.